1. Field of the Invention
This invention relates to a polishing apparatus to be suitably used for the process of preparing a wiring section of a semiconductor device such as a semiconductor memory, which may be a DRAM, or a microprocessor and that of an electrooptical device such as a liquid crystal device or a plasma display device. It also relates to a polishing/cleaning method to be used with such an apparatus as well as to a method of preparing a wiring section.
2. Related Background Art
Firstly a known process of preparing a wiring section of a semiconductor device will be described.
The technique of CMP (chemical mechanical polishing) has been widely used in recent years in the process of manufacturing semiconductor devices and electrooptical devices in order to alleviate the problem of the depth of focus that can arise in the exposure step of photolithgraphy and improve the step coverage of the coat of the device.
FIGS. 14A through 14D of the accompanying drawings are schematic cross sectional side views of a semiconductor device, illustrating different manufacturing steps.
A silicon oxide film 102 is formed by plasma CVD on a semiconductor wafer 100 carrying thereon lower wires 101 that are made of polycrystalline silicon or silicide and operate as components such as a gate electrode. The surface of the produced silicon oxide film may show projections and recesses due to the underlying wires 101 (Step PAS1, FIG. 14A).
Then, the surface of the silicon oxide film is polished by means of a polyurethane polishing pad and a polishing agent prepared by dispersing fine silicon oxide particles in an aqueous solution of KOH until the surface becomes flat (Step PAS2, FIG. 14B).
Subsequently, the work is cleaned by means of an acidic or alkaline chemical agent and a brush. Then, photoresist is applied to the surface of the flattened and smoothed silicon oxide film and expose the photoresist to a beam of KrF excimer laser to produce a latent image of the pattern for forming a contact hole. Thereafter, the latent image is developed to produce a photoresist pattern. The work is then subjected to RIE (reactive ion etching) by using the patterned photoresist as a mask to produce a contact hole 103 (Step PAS3, FIG. 14C).
Thereafter, the photoresist is removed and a silicon-containing aluminum film 105 is formed in the contact hole and on the silicon oxide film (Step PAS4, FIG. 14D).
A multi-wire arrangement can be obtained by repeating the above process.
However, it has recently been found that some of the substances that have adhered to the semiconductor device during the manufacturing process cannot be removed by the above described cleaning method.
For example, a polishing agent obtained by dispersing fine particles of silicon oxide in a potassium-containing treatment agent such as an aqueous solution of potassium hydroxide (KOH) may be used in the above described CMP process. However, the potassium (K) that have adhered to the interlayer insulation film to be polished out of the polishing solution cannot be removed by a chemical cleaning solution of aqueous hydrogen peroxide containing sulfuric acid or ammonium. Nor was it possible to remove it by means of a brush.
Therefore, it is an object of the present invention to provide a polishing apparatus and a polishing method that can effectively and efficiently remove potassium and other alkali metals and also a method of preparing a wiring section.
Another object of the present invention is to provide a polishing apparatus and a polishing method that can remove potassium and other alkali metals without using a high concentration chemical agent typically containing sulfuric acid and also a method of preparing a wiring section.
According to the invention, the above objects and other objects are achieved by providing a polishing apparatus comprising integrally a polishing unit for polishing an object by means of a polishing agent and a cleaning unit for cleaning the polished object, wherein:
the polishing unit and the cleaning unit have means for isolating the internal atmosphere from the external atmosphere; and
the cleaning unit has means for cleaning the polished object by bringing hot pure water or steam of pure water into contact with the polished object.
The cleaning unit may additionally have means for drying the polished object after cleaning it with hot pure water.
The polishing unit and the cleaning unit may be provided with an exhaust port and have means for maintaining the internal atmosphere under negative pressure relative to the external atmosphere.
A potassium-containing polishing agent may be used for polishing the object in the polishing unit.
The cleaning means of the cleaning unit may have a heating means adapted to heat pure water to or above 80xc2x0 C.
The cleaning unit may have means for applying ultrasonic waves with a frequency between 0.8 MHz and 10 MHz to the hot pure water used by the cleaning means.
The hot pure water may contain ozone.
The cleaning unit may have a cleaning member adapted to be brought into contact with the polished object to physically remove any foreign objects adhering to it.
According to the invention, there is also provided a method of polishing/cleaning an object using a polishing apparatus comprising integrally a polishing unit for polishing an object by means of a polishing agent and a cleaning unit for cleaning the polished object, comprising steps of:
polishing the object with the polishing agent; and
cleaning the polished object by bringing hot pure water into contact with it without drying it after polishing it with the polishing agent.
The cleaning method may use a potassium-containing polishing agent.
The polished object to be cleaned by the cleaning method may have a plasma-treated surface.
The hot pure water to be used with the cleaning method may be heated to or above 80xc2x0 C. before brought into contact with the polished object.
Ultrasonic waves with a frequency between 0.8 MHz and 10 MHz may be applied to the hot pure water to be used with the cleaning method.
The polished object to be cleaned by the cleaning method may be a substrate for preparing an electronic device having a wiring section being formed.
The polishing/cleaning method according to the invention may further comprise subsequent to cleaning the polished object:
a first cleaning step of cleaning the object by using ozone-containing ultra-pure water outside said polishing apparatus;
a second cleaning step of cleaning the object by using a solution containing hydrofluoric acid, hydrogen peroxide and a surface active agent and applying ultrasonic waves with a frequency of above 100 KHz;
a third cleaning step of cleaning the object by using ozone-containing ultra-pure water and applying ultrasonic waves of above 100 KHz;
a fourth cleaning step of cleaning the object by using a solution containing hydrofluoric acid; and
a fifth cleaning step of cleaning the object by using ultra-pure water and ultrasonic waves with a frequency of above 100 KHz.
According to the invention, there is also provided a method of making a wired section comprising steps of forming an insulation film, flattening the insulation film, forming a hole in the insulation film, filling an electroconductive material into the hole and forming an electroconductive film on the insulation film, characterized in that:
the step of forming an insulation film includes a step of depositing an insulator by means of a plasma processing technique or a CVD technique; and
the flattening step includes a polishing step using a potassium-containing polishing agent and a cleaning step of bringing hot pure water or steam of pure water into contact with the polished surface of the object without drying the polished surface.
According to the invention, there is also provided a method of making a wired section comprising steps of forming an insulation film, forming a groove in the insulation film, forming an electroconductor at least in the groove and removing part of the electroconductor, characterized in that:
the step of forming an insulation film includes a step of forming an insulator by means of a plasma processing technique or a CVD technique; and
the removing step includes a polishing step using a potassium-containing polishing agent and a cleaning step of bringing hot pure water or steam of pure water into contact with the polished surface of the object without drying the polished surface.
According to the invention, there is also provided a method of making a wired section comprising steps of:
forming an insulation film on a substrate by means of a plasma processing technique or a CVD technique;
polishing the insulation film or an electroconductor formed on the insulation film or in a groove of the insulation film by using a polishing agent; and
cleaning the polished surface of the insulation film by bringing hot pure water or steam of pure water into contact with the polished surface without drying the surface.
The hot pure water may be supplied from the outside of said polishing appratus.
The hot pure water may be supplied by way of the piping system of the plant where said polishing apparatus is arranged.